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The ionization dynamics of Xe cluster was analyzed by extreme ultraviolet (EUV) pump-near infrared (NIR) probe experiments. The experiments were carried out for Xe clusters containing around 5000 atoms on average at the SPring-8 Compact SASE Source (SCSS) test accelerator in Japan. We recorded ion spectra emitted from Xe clusters as a function of the time delay between the EUV and NIR pulses. The ion yields up to highly-charged states were substantially enhanced when Xe clusters excited by the EUV pulses were illuminated by the NIR laser pulses at 1 to 2 ps after the pump pulse, providing a compelling evidence for nano-plasma formation and subsequent NIR absorption via surface plasma resonance. We also observed emergence of low kinetic energy Xe+ at long time delay, which can be attributed to the ionization of excited neutral atoms resulting from the electron-ion recombination in the expanding nano-plasma.

Synopsis Atomic features may appear in the Auger electron spectra after an electron is excited from a core orbital to an antibonding orbital in molecules, as a result of complex competitions among electron and nuclear motions. Relatively weak atomic features were widely discussed in spectator Auger decay processes on top of O 1 s → 3 σ u * excitation in O2 molecules. Thee strong Auger decay processes are heavily-overlapped in the electron spectrum and not discussed up to now. Here, using multi-particle coincidence setup, we separate these Auger decay processes for the first time.

A diamond stamp with a hierarchical pattern was designed for the direct preparation of a periodic nanoarray structure, which was prepared by the reactive ion etching technique with a hierarchical ultrathin alumina membrane (HUTAM) as a mask. The optimal etching conditions for fabricating the diamond stamp were discussed in order to realize a vertical nanopore structure, avoiding structural damage from lateral etching. By using this diamond stamp, a polymer film with the desired hierarchical nanorod array structure can be obtained easily via the simple stamping process, which greatly simplifies the processing procedure. More importantly, the stamp is reusable because of its super-hardness, which ensures the reproducibility of the nanorod array pattern. Another merit is that the smooth surface of the etched diamond can avoid the use of a release agent. Our results prove that this hard stamp can be used for quick preparation of an elaborate periodic nanoarray structure. This study is significant in that it solves the problems of high cost and easy damage of stamps in nanoimprint lithography, and it might inspire more sophisticated applications of such an ordered structure in nanoplasmonics, biochemical sensing and nanophotonic devices.

We have measured electron energy spectra and asymmetry parameters of Ar clusters and Xe clusters illuminated by intense x-rays at 5 and 5.5 keV. A velocity map imaging spectrometer was developed for this purpose and employed at an x-ray free-electron laser facility, SACLA in Japan. The cluster size dependence and the peak fluence dependence of the electron spectra and asymmetry parameters are discussed.

Ag nanoparticles and nanostructured surfaces have been widely used as surface-enhanced Raman scattering (SERS) substrates, which can enhance the Raman signals when molecules are adsorbed on the surface of Ag by the effect of Ag-thiol bonds. In this paper, we propose an efficient method to remove the molecules adsorbed on Ag with sodium borohydride solution, providing a protocol to realize a reproducible and practicable Ag SERS substrate. A theoretical density function theory approach has been used to explain the mechanism of desorption.

By constructing a limited two-dimensional (2D) area to regulate the coalescence of deposited Ag nanoparticles and to change the degree of aggregation of nanoparticles under annealing, a configuration of particles on pillar (POP) was fabricated successfully and high SERS enhancement similar to 'hot spots' was generated on the POP. With the assistance of nanosphere lithography (NSL), we constructed a silicon pillar array with a column diameter of 200 nm and a height of 155 nm. A thin layer of Ag film with a several nanometer thickness was deposited on the top of the silicon pillar array and then was annealed under 200 °C. Differing from the annealed Ag on a flat surface, the aggregation of Ag on the top of a pillar was predominated by the limited area, forming more Ag nanoaggregates. The SERS spectra demonstrated that the POP contributed to higher SERS enhancement than the silicon slide modified by the some thickness annealed Ag film. As a consequence, by means of POP configuration, the lowest SERS detection concentration for 4-mercaptopyridine was able to reach the level of 1.0 × 10(-10) M.

The purpose of this study is to solve the problem of low achievement in fabricating sandwich surface-enhanced Raman scattering (SERS) substrates. We demonstrated a highly efficient sandwich structure by the oriented assembly of metal nanoparticles (NPs) on a periodic hexagonal array of metal nanoprisms with 1,4-benzenedithiol (1,4-BDT) as linkers. The metal nanoprism array was prepared by vacuum deposition of metal on a close-packed polystyrene nanosphere pre-patterned substrate. The metal nanoprism array presents different surface properties from the pits left from the removal of polystyrene nanospheres, which causes linkers to selectively adsorb on the metal nanoprism array and sequentially leads to the oriented immobilization of the second-layer metal NPs, avoiding mismatched orientation. These sandwich SERS substrates were characterized by extinction spectroscopy and atomic force microscopy and their enhancement activity was evaluated under different excitation wavelengths. The sandwich structure greatly increases the achievement of 'hot spots' to almost 100% of all the metal nanoprisms and enables a large amplification of SERS signals by a factor of ten. This method has the advantages of simplicity, high efficiency, high throughput, controllability and high reproducibility. It has significance in both the study of SERS substrates and the development of plasmonic devices.

This paper proposes a non-intrusive and non-invasive method for measuring the gas flow rate in pneumatic industry. A heater unit is fixed on the partial circumference of the external wall of a pipeline and emits specific thermal pulses in a predetermined mode. Two sensors attached to the external wall detect the upstream temperature, and the gas flow can be measured according to the relationship between the flow rate and the dynamic thermal characteristics of the pipeline. To determine the preferable relationship, the temperature field model of the measurement system is built. Then, based on the measurement modes and the corresponding simulations, the objective functions for the gas flow specified on different dynamic thermal characteristics are established. Additionally, the minimum measurement time of the method, named reference time scale, is proposed. Further, robustness tests of the measurement method are derived by considering the influences of multiple factors on the objective functions. The experiments confirm that this method does not need to open the pipeline and disturb the flow regime in order to obtain the data; this method also avoids the typical time-consuming and complex operations, resists ambient temperature disturbance and achieves approximately acceptable results.

The localized plasmon controlled fluorescence has been discussed by comparing the fluorescence enhancement of dyes on different shaped silver nanoparticle self-assembled films. A trilayer structure, composed of a silver nanoparticle monolayer, a proper thickness polyelectrolyte spacing layer and a dye-adsorbed layer, was constructed to study the plasmon enhanced fluorescence properties. The effective coupling of the plasmon band with the excitation or emission of dye resulted in different enhancement factors. Moreover, the plasmon enhanced fluorescence resonance energy transfer (FRET) of two dyes was observed. The FRET efficiency of the spherical silver nanoparticle self-assembled film had a 2.8-fold increase. The improvement of FRET efficiency via localized surface plasmons would increase the sensitivity of FRET-based bioassays.

A facile and reproducible approach for the synthesis of magic-sized CdSe and CdTe nanocrystals is established. The as-synthesized CdSe nanocrystals exhibit strong and fixed absorption features with unusually narrow emission spectra. White-light emission can be achieved by two different routes. One is to mix colours emitted from both the magic-sized nanocrystals and the subsequently transformed regular-sized nanocrystals; the other is to expose the magic-sized nanocrystals to ambient conditions. A systematic study of the nanocrystal formation process shows that monomer activity and injection/growth temperatures are important parameters to the growth kinetics of magic-sized nanocrystals. Variation of these parameters provides tunable existence periods in the hot solution.